Oxygen scavengers, or oxygen absorbers, are used to quickly absorb oxygen from a contained volume of air. Oxygen scavengers can be used in many applications, including in food packaging. By quickly removing oxygen from food packaging, the shelf life of perishable goods is improved. When used in food packaging, oxygen scavengers prevent food color change and slow the growth of bacteria.
Oxygen scavengers often operate by reacting an oxygen reducing agent with oxygen. One common oxygen reducing agent is iron. The reaction of iron and oxygen may be represented by the following formula:4Fe+O2→2Fe2O3 The unaided oxidation of iron is rather slow, however. Thus, it is advantageous to include a catalyst to speed the reaction. One such catalyst is water. In the presence of water, the reaction of iron and oxygen may be represented by the following formulae:2Fe+O2+2H2O→2Fe(OH)2 4Fe(OH)2+O2→2H2O+2Fe2O3·H2O
Another such catalyst is an acid. A lowered pH improves the speed of oxidation. However, some acid catalyzed oxygen scavengers produce hydrogen gas and other gasses as a byproduct of oxygen absorption. The production of gas is undesirable in food packaging, as it tends to cause packaging to bloat.